1. Field of the Invention
The present invention relates to a rotor of an electric rotary machine constructed such that a rotor winding is buried in slots which open toward the outer peripheral surface of the rotor core, and particularly to a rotor the winding of which is easy to be directly wound by a winding machine.
2. Description of the Prior Art
An induction motor is inadequate for driving a load which needs a speed change. However, an induction motor is still widely used, in combination with an electrical or mechanical speed change gear, for driving a load which is required to be varied in speed. An induction motor used in combination with an electrical or mechanical speed change gear, however, has very poor efficiency. From the standpoint of saving electric power consumption, it is desirable that a direct current motor which is easily controlled in speed be used for driving such a load of the type which requires speed variation. The application of a D.C. motor to such load has not yet become widespread, because the direct current motor is expensive. In general, an electrical machine having a rotor the winding of which is buried in slots which open toward the outer peripheral surface of the rotor core, as seen not only in the D.C. motor but also in a repulsion start induction motor, is very expensive. The reason for this is that the winding operation requires a number of manufacturing steps and in addition, since the rotor, unlike the stator, is affected by centrifugal force, the winding operation needs high skill.
Various researches have been made for mechanization of the operation of burying the winding conductors in the rotor core slots, but such mechanization has been put into practice only for small-sized motors of 1 kW or below. The difficulty which has been encountered in mechanizing the winding operation is how the coil end is made dense or compact. If the coil end is not dense, the entire length of the motor in the axial direction becomes large, raising the cost. In addition, the rotor winding is affected by the centrifugal force and consequently the conductors thereof are moved by such force. Thus, there is a fear that dielectric breakdown may be caused.